The invention relates to a dosing device for fluids used in infusion or transfusion systems comprising a flexible fluid line transversing a housing and a pressure element supported in the housing to compress the fluid line.
To perform infusions or transfusions, a reservoir containing the infusion or transfusion fluid and having a downwardly directed aperture, as well as a connected fluid line, is suspended as high as is considered necessary to ensure that the fluid pressure in the line is higher than the vein pressure of the patient. The fluid is delivered first to an intermediate container in the fluid line and then from there to the patient. Due to the different marginal conditions, e.g. the vein pressure of the patient, the viscosity of the fluid and the varying filling height of the fluid container and due to the fluid dosages determined therapeutically, it is necessary to accurately adjust the rate of flow of the fluid.
There have been known dosing means of the above mentioned type comprising a fluid line extending through a housing and a clamping element which consists of a roller guided in the housing and pressing on the hose cross section (DE-OS No. 26 37 495). The dosage amount usually determined by the number of fluid drops dripping per unit of time into the intermediate container cannot be kept constant for a long period with such a device because the PVC-hoses usually applied may deform due to their creep tendency (cold flow property). Problems will develop above all if the dosage amount needs to be increased leading to a longer compression of the fluid line than previously considered necessary, because the tough-elastic relaxation behavior present as a result of hysteresis of the plastic line inhibits a quick recovery of the original line cross section. Hence, even with constant adjustment a constant dosage cannot be realized with such dosing devices.
There has also been provided a dosing means comprising a housing and a substantially cylindrical valve chamber provided therein, with two connecting pieces having a respective channel and projecting radially from the housing or valve chamber in opposite directions, and a plug rotatable with a handle and sealingly disposed in the valve chamber. In the jacket surface of the plug, a passage is provided which when subjected to the rotary position of the plug admits, between the connecting pieces, flow cross sections of different dimensions. (DE-OS No. 27 35 955). Such dosing means are involved with a considerable constructional expenditure to ensure a safe sealing of the dosing means against air access.
Therefore, it is an object of the present invention to provide a fluid dosing means for infusion or transfusion devices which will overcome the above noted and other disadvantages.
It is another object of the present invention to provide a dosing means which permits an accurate, time-constant and reproducibly adjustable dosing of fluids.